In many aerospace applications, particularly airplane manufacture, whenever a rivet or other fastener will be installed in an assembly, a sealant must be applied around the fastener at the same time. Currently, aircraft sealants are two-part sealants that need to be mixed accurately and used within a certain amount of time. The mixed sealant is hand applied to fasteners and the “wet” fasteners are then installed. Excess sealant is wiped off and disposed of along with unused sealant.
The labor spent applying sealant to rivets and fasteners in aircraft manufacture and repair is a significant cost and time factor. To put the wasted time and effort into perspective, the C-17, the largest military aircraft currently in production, has over 1.4 million rivets and fasteners in each aircraft. It is estimated that there are on the order of 10 million wet installed fasteners going into military and commercial aircraft per year in the U.S. alone. Eliminating or greatly reducing the number of wet fastener installations could save tens of thousands of labor hours and millions of dollars on the manufacture of just one C-17 aircraft.
In addition, the process variability associated with “wet” installations is large. The amount of sealant applied, and areas of the rivet/fastener coated or uncoated vary widely with the installer. Excess sealant is often applied, resulting in additional time and expense for clean up of the excess sealant. Further, prior art wet installation creates toxic waste disposal problems because excess and unused sealant often contains toxic materials such as Chromium.
A number of attempts have been made at developing automated or semi-automated methods for coating rivets and fasteners over the past 30 years, but all were either unsuccessful or suffer from significant shortcomings.
What is needed is an improved fastener suitable for use in airplane manufacture that does not require the expensive, wasteful, and time-consuming wet installation methods presently in use. Also needed are methods of producing such fasteners in commercially viable quantities.